Such electric heating devices are used to counteract icing up of the rotor blades. The devices are made of an electrically conducting material and during operation a heating current flows through them and brings about heating of the heating device. As a result, on the one hand, ice which has already adhered is thawed (de-icing), and, on the other hand, icing can be prevented (anti-icing).
In order to achieve the desired effect, a sufficient temperature difference with respect to the surroundings must be achieved in the entire heatable surface region. At the same time, excessive heating is to be avoided, in particular in order to prevent damage to the rotor blade. Heating which goes beyond the necessary extent is also to be avoided in order to keep the energy consumption of the heating device as low as possible.
DE 20 2012 101 705 U1 has disclosed a wind turbine rotor blade having an electric heating device which is energized via two electrodes running in the longitudinal direction of the heating device and which is to have a gel layer.
WO 2011/127996 A1 has disclosed a wind turbine rotor blade having an electric heating device which has a plurality of sections partially connected in series. The electric heating device runs in the form of a loop from a root-blade-side end as far as a blade-tip-side end and back and is connected to electric leads in the region of the blade root.
U.S. Pat. Nos. 5,947,418 and 6,338,455 have disclosed rotor blades for helicopters which have a plurality of strips which run in the longitudinal direction of the rotor blades and whose blade-tip-side ends are connected to one another and whose blade-root-side ends are connected to electric connecting leads. A heating current also flows through them in a loop shape from the blade root as far as the blade tip and back.
WO 2011/096851 A1 has disclosed a wind turbine rotor blade having an electric heating device which is composed of different heating elements and leads which each have carbon nanotubes. The heatable surface is divided into numerous fields, each of which is assigned an icing up sensor. If icing up is detected in one of the fields, this field is to be able to be heated selectively.
United States patent application publication 2014/0348654 has disclosed a wind turbine rotor blade having an electric heating device which is supplied with a heating current via two outer electric leads. The electric leads serve at the same time as lightning arrestor leads.
EP 2 843 228 A1 has disclosed a wind turbine rotor blade having an electric heating element which is constructed from bundles of electrically conductive fibers which each form an individual current path. The power supply is provided via two electric leads which run in the longitudinal direction of the rotor blade and are connected to the individual fiber bundles.